Material for printed circuit board, metal laminate, methods for producing them, and method for producing printed circuit board

ABSTRACT

A material for a printed circuit board, which is a film composed of a fluorinated resin layer, where the fluorinated resin layer contains a composition containing a fluorinated copolymer having at least one functional group selected from a carbonyl group-containing group, a hydroxy group, an epoxy group and an isocyanate group, has a melt flow rate of at most 15 g/10 min measured at 372° C. under a load of 49N, and has a storage elastic modulus of at least 650 MPa.

TECHNICAL FIELD

The present invention relates to a material for a printed circuit board,a metal laminate, methods for producing them, and a method for producinga printed circuit board.

BACKGROUND ART

In recent years, along with weight reduction, size reduction and highdensification of electronic products, demand for various types ofprinted circuit boards is expanding. Particularly, demand for flexiblemetal laminates is increasing. A flexible metal laminate is also calleda flexible printed circuit board or the like.

A flexible printed circuit board is produced e.g. by a method of bondinga metal foil on an insulating film as a substrate by means of anadhesive material by heating and contact bonding, and etching the metalfoil to form a circuit.

As the insulating film, a polyimide film or the like is preferably used,and as the adhesive material, e.g. an epoxy or acrylic thermosettingadhesive is commonly used.

The thermosetting adhesive is advantageous in that bonding at arelatively low temperature is possible, however, it is considered that aflexible printed circuit board having an adhesive layer composed of athermosetting adhesive can hardly meet required demands such as heatresistance, flexibility and electrical reliability which are consideredto be stricter in the future.

Accordingly, as a flexible printed circuit board using no thermosettingadhesive, a flexible printed circuit board having a metal foil directlybonded to an insulating film has been proposed. Further, for example,Patent Document 1 proposes a flexible printed circuit board using athermoplastic polyimide for the adhesive layer.

Further, Patent Document 2 proposes a flexible printed circuit boardhaving a reinforcing layer of e.g. a polyimide resin and an electricalconductive layer such as a copper foil laminated via an electricalinsulator layer made of a fluorinated copolymer having an acid anhydrideresidue. The fluorinated copolymer constituting the electrical insulatorlayer has adhesion due to the acid anhydride residue, and accordinglythe electrical insulator layer functions also as an adhesive layer.Further, by using the fluorinated copolymer, which is excellent inelectrical properties, for a layer in contact with the electricalconductive layer (metal foil), excellent electrical reliability will beobtained as compared with a case where a thermoplastic polyimide is usedfor the adhesive layer.

However, a flexible printed circuit board having a layer of thefluorinated copolymer as an insulating layer, is likely to be warped athigh temperature.

Patent Document 3 discloses a technique of mixing a thermoplasticpolyimide with the fluorinated copolymer to improve heat resistantstiffness. However, even by the method of mixing another resin, thewarpage cannot sufficiently be suppressed at a high temperature region(150 to 200° C.).

Further, it is known that electrical properties such as dielectricconstant which are excellent characteristics of a fluororesin decreaseif a thermoplastic polyimide is mixed with a fluorinated copolymer as inPatent Document 3. Particularly for applications for high frequency, thematerial of an insulating layer to be in a direct contact with the metallayer is required to have a low dielectric constant and a low dielectricloss tangent and excellent electrical properties. Accordingly, it isdesired to improve properties such as stiffness of a fluorinatedcopolymer to be used for an insulating layer without mixing anothermaterial such as a thermoplastic polyimide as far as possible.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP-A-2013-67810

Patent Document 2: WO2006/067970

Patent Document 3: WO2012/070401

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made under the above circumstances, andit is an object of the present invention to provide a material for aprinted circuit board which is less likely to be warped at a hightemperature region (150 to 200° C.) while it maintains electricalproperties, a metal laminate, methods for producing them, and a methodfor producing a printed circuit board.

Solution to Problem

The present invention has the following aspects [1] to [15].

[1] A method for producing a material for a printed circuit board, whichcomprises subjecting a film (A) provided with a fluorinated resin layercomposed of a composition containing a fluorinated copolymer (a) to aheat treatment to obtain a material for a printed circuit board, wherein

the film (A) is a film (A1) consisting of the fluorinated resin layer oran adhesive film (A2) having the fluorinated resin layer directlylaminated on at least one side of a heat resistant resin film,

the fluorinated copolymer (a) has at least one type of functional groupselected from the group consisting of a carbonyl group-containing group,a hydroxy group, an epoxy group and an isocyanate group, has a meltingpoint of from 280 to 320° C., and has a melt flow rate of at least 2g/10 min measured at 372° C. under a load of 49 N. and

the heat treatment of the film (A) is carried out at a temperature of atleast 250° C. and lower by at least 5° C. than the melting point of thefluorinated copolymer (a) so that the ratio of the following MFR(II) tothe following MFR(I) [MFR(II)/MFR(I)] is from 0.05 to 0.5 and that thefollowing MFR(II) is at most 15 g/10 min:

MFR(II): the melt flow rate of the fluorinated resin layer before theheat treatment measured at 372° C. under a load of 49 N; and

MFR(II): the melt flow rate of the fluorinated resin layer after theheat treatment measured at 372° C. under a load of 49 N.

[2] The method for producing a material for a printed circuit boardaccording to [1], wherein the fluorinated copolymer (a) has at least acarbonyl group-containing group as the functional group, and thecarbonyl group-containing group is at least one member selected from thegroup consisting of a group having a carbonyl group between carbon atomsin a hydrocarbon group, a carbonate group, a carboxy group, a haloformygroup, an alkoxycarbonyl group and an acid anhydride residue.[3] The method for producing a material for a printed circuit boardaccording to [1] or [2], wherein the content of the functional group isfrom 10 to 60,000 groups per 1×10⁸ carbon atoms in the main chain of thefluorinated copolymer (a).[4] A material for a printed circuit board, which is a film consistingof a fluorinated resin layer, wherein the fluorinated resin layer iscomposed of a composition containing a fluorinated copolymer having atleast one type of functional group selected from the group consisting ofa carbonyl group-containing group, a hydroxy group, an epoxy group andan isocyanate group, has a melt flow rate of at most 15 g/10 minmeasured at 372° C. under a load of 49 N, and has a storage elasticmodulus of at least 650 MPa.[5] A material for a printed circuit board, which is an adhesive filmhaving a fluorinated resin layer directly laminated on at least one sideof a heat resistant resin film, wherein

the fluorinated resin layer is composed of a composition containing afluorinated copolymer having at least one type of functional groupselected from the group consisting of a carbonyl group-containing group,a hydroxy group, an epoxy group and an isocyanate group, and has a meltflow rate of at most 15 g/10 min measured at 372° C. under a load of 49N, and

the linear expansion coefficient of the material for a printed circuitboard at from 150 to 200° C. is within a range of from 0 to 25 ppm/° C.

[6] A method for producing a metallaminate, which comprises producing amaterial for a printed circuit board by the method as defined in any oneof [1] to [3], and directly laminating a metal layer on the fluororesinlayer of the material for a printed circuit board.[7] A method for producing a printed circuit board, which comprisesproducing a metal laminate by the method as defined in [6], and etchingthe metal layer to form a patterned circuit.[8] The method for producing a printed circuit board according to [7],wherein the formed patterned circuit is soldered by a soldering iron.[9] A method for producing a metal laminate, which comprises subjectinga metal laminate precursor comprising an adhesive film (A2) having afluorinated resin layer composed of a compound containing a fluorinatedcopolymer (a) directly laminated on at least one side of a heatresistant resin film, and a metal layer directly laminated on the atleast one fluorinated resin layer, to a heat treatment to obtain a metallaminate, wherein

the fluorinated copolymer (a) has at least one type of functional groupselected from the group consisting of a carbonyl group-containing group,a hydroxy group, an epoxy group and an isocyanate group, has a meltingpoint of from 280 to 320° C., and has a melt flow rate of at least 2g/10 min measured at 372° C. under a load of 49 N, and

the heat treatment is carried out at a temperature of at least 250° C.and lower by at least 5° C. than the melting point of the fluorinatedcopolymer (a) so that the ratio of the following MFR(VI) to thefollowing MFR(V) [MFR(VI)/MFR(V)] is from 0.05 to 0.5 and that thefollowing MFR(VI) is at most 15 g/10 min:

MFR(V): the melt flow rate of the fluorinated resin layer before theheat treatment measured at 372° C. under a load of 49 N; and

MFR(VI): the melt flow rate of the fluorinated resin layer after theheat treatment measured at 372° C. under a load of 49 N.

[10] The method for producing a metal laminate according to [9], whereinthe fluorinated copolymer (a) has at least a carbonyl group-containinggroup as the functional group, and the carbonyl group-containing groupis at least one member selected from the group consisting of a grouphaving a carbonyl group between carbon atoms in a hydrocarbon group, acarbonate group, a carboxy group, a haloformyl group, an alkoxycarbonylgroup and an acid anhydride residue.[11] The method for producing a metal laminate according to [9] or [10],wherein the content of the functional group is from 10 to 60,000 groupsper 1×10⁶ carbon atoms in the main chain of the fluorinated copolymer(a).[12] The method for producing a metal laminate according to any one of[9] to [11], wherein the fluorinated resin layer has a thickness of from1 to 20 μm.[13] A metal laminate comprising an adhesive film having a fluorinatedresin layer directly laminated on at least one side of a heat resistantresin film, and a metal layer directly laminated on the at least onefluorinated resin layer, wherein

the fluorinated resin layer is composed of a composition containing afluorinated copolymer having at least one type of functional groupselected from the group consisting of a carbonyl group-containing group,a hydroxy group, an epoxy group and an isocyanate group, and has a meltflow rate of at most 15 g/10 min measured at 372° C. under a load of 49N, and

the linear expansion coefficient of the adhesive film at from 150 to200° C. is within a range of from 0 to 25 ppm/° C.

[14] A method for producing a printed circuit board, which comprisesproducing a metal laminate by the method as defined in [9] to [12], andetching the metal layer to form a patterned circuit.[15] The method for producing a printed circuit board according to [14],wherein the patterned circuit is soldered by a soldering iron.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a materialfor a printed circuit board which is less likely to be warped in a hightemperature region (150 to 200° C.), while it maintains electricalproperties, a method for producing a material for a printed circuitboard, a metal laminate, a method for producing a metal laminate, and amethod for producing a printed circuit board.

DESCRIPTION OF EMBODIMENTS

The following definitions of terms apply throughout the specificationincluding Claims.

The “melt flow rate (hereinafter sometimes referred to as MFR)” is avalue measured at 372° C. under a load of 49 N.

The term “directly laminated” means that two layers are laminated indirect contact with each other without another layer.

A “constituting unit” means a unit derived from a monomer, as formed bypolymerization of the monomer. A constituting unit may be a unit formeddirectly by a polymerization reaction or may be a unit having part of aunit in a polymer converted to another structure by treating thepolymer.

A “fluorinated monomer” means a monomer having a fluorine atom in itsmolecule, and a “non-fluorinated monomer” means a monomer having nofluorine atom in its molecule.

A “main chain” means a moiety which is the principal carbon chain in achain compound and which corresponds to a backbone having the maximumcarbon number.

A “carbonyl group-containing group” means a group containing a carbonylgroup (—C—(═O)—) in its structure.

First Embodiment

According to a first embodiment, the present invention provides a methodfor producing a material for a printed circuit board, which comprisessubjecting a film (A) provided with a fluorinated resin layer composedof a composition containing a specific fluorinated copolymer (a) to aheat treatment to obtain a material for a printed circuit board.

The film (A) is a film (A1) consisting of the fluorinated resin layer,or an adhesive film (A2) having the fluorinated resin layer directlylaminated on at least one side of the heat resistant resin film.

In the first embodiment, the heat treatment is carried out at atemperature of at least 250° C. and lower by at least 5° C. that themelting point of the fluorinated copolymer (a) so that the ratio of MFR(II) to MRF (I) [MFR(II)/MFR(I)] is from 0.05 to 0.5 and that MFR(II) isat most 15 g/10 min, where MFR(I) is the melt flow rate of thefluorinated resin layer before the heat treatment, and MFR(II) is themelt flow rate of the fluorinated resin layer after the heat treatment.

The production method according to the first embodiment may comprise,after the material for a printed circuit board is produced by the abovestep of conducting a heat treatment (hereinafter sometimes referred toas step (I)), a step of directly laminating a metal layer on thefluorinated resin layer of the material for a printed circuit board toproduce a metal laminate (hereinafter sometimes referred to as step(II)), a step of etching the metal layer to form a patterned circuitthereby to produce a printed circuit board (hereinafter sometimesreferred to as step (III)) and a step of soldering the formed patternedcircuit by a soldering iron (hereinafter sometimes referred to as step(IV)).

(Film (A))

The film (A) is a single layer film (A1) consisting of the fluorinatedresin layer or a multilayer adhesive film (A2) having the fluorinatedresin layer directly laminated on at least one side of a heat resistantresin film,

<Fluorinated Resin Layer>

The fluorinated resin layer is a layer obtained by forming a compositioncontaining a fluorinated copolymer (a).

The fluorinated copolymer (a) used for forming the fluorinated resinlayer has MFR of at least 2 g/10 min. When MFR is at least 2 g/10 min,the fluorinated copolymer (a) has melt flowability and is capable ofmelt forming.

MFR of the fluorinated copolymer (a) is preferably from 2 to 1,000 g/10min, more preferably from 2 to 100 g/10 min, further preferably from 2to 30 g/10 min, most preferably from 5 to 20 g/10 min. When MFR is atleast the lower limit value of the above range, the fluorinatedcopolymer (a) is excellent in the forming property, and the fluorinatedresin layer will be excellent in the surface smoothness and theappearance. When MFR is at most the upper limit value of the aboverange, the fluorinated resin layer will be excellent in the mechanicalstrength.

Further, when the fluorinated copolymer (a) has MFR of from 2 to 15 g/10min, the heat resistance against the soldering iron tends to improve.

MFR is an index for the molecular weight of the fluorinated copolymer(a), and high MFR indicates a low molecular weight, and low MFRindicates a high molecular weight. The molecular weight of thefluorinated copolymer (a), and thus MFR, can be adjusted by theconditions for producing the fluorinated copolymer (a). For example, ifthe polymerization time is shortened at the time of polymerization ofthe monomer, MFR tends to increase. On the other hand, in order toreduce MFR, a method of subjecting the fluorinated copolymer (a) to aheat treatment to form a crosslinked structure thereby to increase themolecular weight; or a method of reducing the amount of a radicalpolymerization initiator used for production of the fluorinatedcopolymer (a) may, for example, be mentioned.

The melting point of the fluorinated copolymer (a) used for forming thefluorinated resin layer is from 280° C. to 320° C., preferably from 295°C. to 315° C., particularly preferably from 295° C. to 310° C.

When the melting point of the fluorinated copolymer (a) is at least thelower limit value of the above range, excellent heat resistance will beachieved, and when the after-described printed circuit board issubjected to solder reflow at high temperature or a soldering iron athigh temperature is pressed against the printed circuit board, swelling(foaming) of the fluorinated resin layer due to heat tends to besuppressed.

The melting point of the fluorinated copolymer (a) may be adjusted e.g.by the types and the contents of the constituting units constituting thefluorinated copolymer (a) the molecular weight, etc. For example, thehigher the ratio of the after-described constituting units (m1), themore the melting point tends to increase.

The fluorinated copolymer (a) has at least one type of functional group(hereinafter sometimes referred to as functional group (i)) selectedfrom the group consisting of a carbonyl group-containing group, ahydroxy group, an epoxy group and an isocyanate group. By the functionalgroup (i), the fluorinated resin layer containing the fluorinatedcopolymer (a) will be favorably attached to the after-described heatresistant resin film and the metal layer and function as an adhesivelayer.

The functional group (i) is present preferably at least either one ofthe main chain terminal and the side chains of the fluorinated copolymer(a). The fluorinated copolymer (a) may contain one type or two or moretypes of the functional group (i).

The fluorinated copolymer (a) preferably contains as the functionalgroup (i) at least a carbonyl group-containing group.

A carbonyl group-containing group is a group containing a carbonyl group(—C(═O)—) in its structure and may, for example, be a group having acarbonyl group between carbon atoms in a hydrocarbon group, a carbonategroup, a carboxy group, a haloformyl group, an alkoxycarbonyl group oran acid anhydride residue.

The hydrocarbon group may, for example, be a C₂₋₈ alkylene group. Thenumber of carbon atoms in the alkylene group is a number of carbon atomsnot including the carbonyl group. The alkylene group may be linear orbranched.

The haloformyl group is represented by —C(═O)—X (wherein X is a halogenatom). The halogen atom in the haloformyl group may, for example, be afluorine atom or a chlorine atom, and is preferably a fluorine atom.That is, the haloformyl group is preferably a fluoroformyl group (alsocalled a carbonyl fluoride group).

The alkoxy group in the alkoxycarbonyl group may be linear or branched,and is preferably a C₁₋₈ alkoxy group, particularly preferably a methoxygroup or an ethoxy group.

The content of the functional group (i) in the fluorinated copolymer (a)is preferably from 10 to 60,000 groups, more preferably from 100 to50,000 groups, further preferably from 100 to 10,000 groups,particularly preferably from 300 to 5,000 groups per 1×10⁶ carbon atomsin the main chain of the fluorinated copolymer (a). When the content ofthe functional group (i) is at least the lower limit value of the aboverange, the adhesion of the fluorinated resin layer containing thefluorinated copolymer (a) to the heat resistant resin film and the metallayer will be more excellent, and when it is at most the upper limitvalue of the above range, a high level of adhesion to the heat resistantresin film will be obtained at a low processing temperature.

The content of the functional group (i) may be measured by means of e.g.nuclear magnetic resonance (NMR) analysis or infrared absorptionspectrum analysis. For example, by means of e.g. infrared absorptionspectrum analysis as disclosed in JP-A-2007-314720, the proportion (mol%) of the constituting units having the functional group (i) in all thestructural units constituting the fluorinated copolymer (a) isdetermined, and from the proportion, the content of the functional group(i) can be calculated.

The fluorinated copolymer (a) is preferably a copolymer containingconstituting units (m1) based on tetrafluoroethylene (hereinaftersometimes referred to as “TFE”), constituting units (m2) based on acyclic hydrocarbon monomer having an acid anhydride residue and apolymerizable unsaturated bond, and constituting units (m3) based on afluorinated monomer (excluding TFE).

Here, the acid anhydride residue in the constituting units (m2)corresponds to the functional group (i).

The fluorinated copolymer (a) may have the functional group (i) as themain chain terminal group. The functional group (i) as a main chainterminal group is preferably e.g. an alkoxycarbonyl group, a carbonategroup, a hydroxy group, a carboxy group, a fluoroformyl group or an acidanhydride residue. Such a functional group may be introduced by propertyselecting the radical polymerization initiator, the chain transferagent, etc. used at the time of producing the fluorinated copolymer (a).

The cyclic hydrocarbon monomer having an acid anhydride residue and apolymerizable unsaturated bond for forming the constituting units (m2)may, for example, be itaconic anhydride (hereinafter sometimes referredto as “IAH”), citraconic anhydride (hereinafter sometimes referred to as“CAH”), 5-norbornene-2,3-dicarboxylic anhydride (hereinafter sometimesreferred to as “NAH”) or maleic anhydride. They may be used alone or incombination of two or more.

Among them, preferred is at least one member selected from the groupconsisting of IAH, CAH and NAH. In such a case, the fluorinatedcopolymer (a) containing an acid anhydride residue may readily beproduced without employing a special polymerization method (seeJP-A-11-193312) which is required when maleic anhydride is used.

Between IAH, CAH and NAH, NAH is preferred in view of more excellentadhesion to the heat resistant resin film.

The fluorinated monomer for forming the constituting units (m3) ispreferably a fluorinated compound having one polymerizable double bond.It may, for example, be a fluoroolefin (excluding TFE) such as vinylfluoride, vinylidene fluoride (hereinafter sometimes referred to as“VdF), trifluoroethylene, chlorotrifluoroethylene (hereinafter sometimesreferred to as “CTFE” or hexafluoropropylene (hereinafter sometimesreferred to as “HFP”), CF₂═CFOR^(f1)” (wherein R^(f1) is a C₁₋₁₀perfluoroalkylene group which may contain an oxygen atom between carbonatoms), CF₂═CFOR^(f2)SO₂X¹ (wherein R^(f2) is a C₁₋₁₀ perfluoroalkylenegroup which may contain an oxygen atom between carbon atoms, and X¹ is ahalogen atom or a hydroxy group), CF₂═CFOR^(f3)CO₂X² (wherein R^(f3) isa C₁₋₁₀ perfluoroalkylene group which may contain an oxygen atom betweencarbon atoms, and X² is a hydrogen atom or a C₁₋₃ alkyl group),CF₂═CF(CF₂)_(p)OCF═CF₂ (wherein p is 1 or 2), CH₂═CX(CF₂)_(q)X⁴ (whereinX³ is a hydrogen atom or a fluorine atom, q is an integer of from 2 to10, and X⁴ is a hydrogen atom or a fluorine atom) orperfluoro(2-methylene-4-methyl-1,3-dioxolane).

Among such fluorinated monomers, preferred is at least one memberselected from the group consisting of VdF, CTFE, HFP, CF₂═CFOR^(f1) andCH₂═CX³(CF₂)_(q)X⁴, more preferred is CF₂═CFOR^(f1) or HFP.

CF₂═CFOR^(f1) may, for example, be CF₂═CFOCF₂CF₃, CF₂═CFOCF₂CF₂CF₃,CF₂=CFOCF₂CF₂CF₂CFs or CF₂═CFO(CF₂)₈F, and is preferablyCF₂═CFOCF₂CF₂CF₃ (hereinafter sometimes referred to as “PPVE”).

CH₂═CX³(CF₂)_(q)X⁴ may, for example, be CH₂═CH(CF₂)₂F, CH₂═CH(CF₂)₃F,CH₂═CH(CF₂)₄F, CH₂═CF(CF₂)₃H or CH₂═CF(CF₂)₄H, and is preferablyCH₂═CH(CF₂)₄F or CH₂═CH(CF₂)₂F.

The fluorinated copolymer (a) preferably comprises, based on the totalmolar amount of the constituting units (m1), (m2) and (m3), from 50 to99.89 mol % of the constituting units (m1), from 0.01 to 5 mol % of theconstituting units (m2) and from 0.1 to 49.99 mol % of the constitutingunits (m3), more preferably from 50 to 99.4 mol % of the constitutingunits (m1), from 0.1 to 3 mol % of the constituting units (m2) and from0.5 to 49.9 mol % of the constituting units (m3), particularlypreferably from 50 to 98.9 mol % of the constituting units (m1), from0.1 to 2 mol % of the constituting units (m2) and from 1 to 49.9 mol %of the constituting units (m3).

When the contents of the respective constituting units are within theabove ranges, the fluorinated copolymer (a) will be excellent in theheat resistance and the chemical resistance, and the fluorinated resinlayer will be excellent in the coefficient of elasticity at hightemperature.

Particularly when the content of the constituting units (m2) is withinthe above range, the amount of the acid anhydride residue in thefluorinated copolymer (a) will be appropriate, and the fluorinated resinlayer will be excellent in the adhesion to the heat resistant resin filmand the metal layer. Further, the after-described effect of lowering thelinear expansion coefficient in high temperature region will besufficiently obtained.

When the content of the constituting units (m3) is within the aboverange, the fluorinated copolymer (a) will be excellent in formingproperty, and the fluorinated resin layer will be more excellent inmechanical properties such as flexing resistance. The contents of therespective constituting units may be calculated by means of e.g. moltenNMR analysis, fluorine content analysis and infrared absorption spectrumanalysis of the fluorinated copolymer (a).

In a case where the fluorinated copolymer (a) comprises the constitutingunits (m1), (m2) and (m3), the content of the constituting units (m2)being 0.01 mol % based on the total molar amount of the constitutingunits (m1), (m2) and (m3) corresponds to a content of the acid anhydrideresidue being 100 residues per 1×10⁶ carbon atoms in the main chain ofthe fluorinated copolymer (a). The content of the constituting units(m2) being 5 mol % based on the total molar amount of the constitutingunits (m1), (m2) and (m3) corresponds to a content of the acid anhydrideresidue in the fluorinated copolymer (a) being 50,000 residues per 1×10⁶carbon atoms in the main chain of the fluorinated copolymer (a).

The fluorinated copolymer (a) having the constituting units (m2) maycontain constituting units based on a dicarboxylic acid (such asitaconic acid, citraconic acid, 5-norbornene-2,3-dicarboxylic acid ormaleic acid) corresponding to the acid anhydride residue due to partialhydrolysis of the cyclic hydrocarbon monomer having an acid anhydrideresidue and a polymerizable unsaturated bond. In a case where thefluorinated copolymer (a) contains the constituting units based on thedicarboxylic acid, the content of such constituting units is included inthe content of the constituting units (m2).

The fluorinated copolymer (a) may have constituting units (m4) based ona non-fluorinated monomer (excluding the cyclic hydrocarbon monomerhaving an acid anhydride residue and a polymerizable unsaturated bond)in addition to the above-described constituting units (m1) to (m3).

Such a non-fluorinated monomer is preferably a non-fluorinated compoundhaving one polymerizable double bond and may, for example, be an olefinhaving at most 3 carbon atoms such as ethylene or propylene, or a vinylester such as vinyl acetate. They may be used alone or in combination oftwo or more. Among them, preferred is ethylene, propylene or vinylacetate, particularly preferred is ethylene.

In a case where the fluorinated copolymer (a) has the constituting units(m4), the content of the constituting units (m4) is preferably from 5 to90 mol %, more preferably from 5 to 80 mol %, most preferably from 10 to65 mol % based on the total molar amount of the constituting units (m1),(m2) and (m3) being 100 mol %.

Based on the total molar amount of all the constituting units in thefluorinated copolymer (a) being 100 mol %, the total molar amount of theconstituting units (m1) to (m3) is preferably at least 60 mol %, morepreferably at least 65 mol %, most preferably at least 68 mol %. Apreferred upper limit value is 100 mol %.

As preferred specific examples of the fluorinated copolymer (a), aTFE/PPVE/NAH copolymer, a TFE/PPVE/IAH copolymer, a TFE/PPVE/CAHcopolymer, a TFE/HFP/IAH copolymer, a TFE/HFP/CAH copolymer, aTFE/VdF/IAH copolymer, a TFE/VdF/CAH copolymer, aTFE/CH₂═CH(CF₂)₄F/IAH/ethylene copolymer, aTFE/CH₂═CH(CF₂)₄F/CAH/ethylene copolymer, aTFE/CH₂═CH(CF₂)₂F/IAH/ethylene copolymer and aTFE/CH₂═CH(CF₂)₂F/CAH/ethylene copolymer may be mentioned.

The fluorinated copolymer (a) may be produced by a conventional method.

As a method for producing the fluorinated copolymer (a) having thefunctional group (i), for example, (1) a method of using a monomerhaving the functional group (i) when the fluorinated copolymer (a) isproduced by a polymerization reaction, (2) a method of using a radicalpolymerization initiator or chain transfer agent having the functionalgroup (i) to produce the fluorinated copolymer (a) by a polymerizationreaction, (3) a method of heating a fluorinated copolymer having nofunctional group (i) to partially thermally decompose the fluorinatedcopolymer to form a reactive functional group (such as a carbonyl group)thereby to obtain the fluorinated copolymer (a) having the functionalgroup (i), or (4) a method of graft-polymerizing a monomer having thefunctional group (i) to a fluorinated copolymer having no functionalgroup (i) to introduce the functional group (i) to the fluorinatedcopolymer, may, for example, be mentioned. The method for producing thefluorinated copolymer (a) is particularly preferably the method (1).

As polymerization conditions, etc., for example, conditions as disclosedin JP-A-2014-224249, paragraphs [0034] to [0039] may be mentioned.

The fluorinated resin layer is one obtained by forming a compositioncontaining the fluorinated copolymer (a). The composition may containone type or two or more types of the fluorinated copolymer (a).

The content of the fluorinated copolymer (a) in the fluorinated resinlayer (that is, the content of the fluorinated copolymer (a) in thecomposition containing the fluorinated copolymer (a)) is preferably atleast 50 mass %, more preferably at least 80 mass % based on the totalmass of the fluorinated resin layer in view of the adhesion of thefluorinated resin layer to the heat resistant resin film and the metallayer. The upper limit of the content is not particularly limited andmay be 100 mass %.

The composition containing the fluorinated copolymer (a) may contain aresin other than the fluorinated copolymer (a) within a range not toimpair the effects of the present invention as the case requires.

The resin other than the fluorinated copolymer (a) is not particularlylimited within a range not to impair the electrical reliability. It may,for example, be a fluorinated copolymer other than the fluorinatedcopolymer (a), an aromatic polyester, a polyamide imide or athermoplastic polyimide. The fluorinated copolymer other than thefluorinated copolymer (a) may, for example, be atetrafluoroethylene/fluoroalkyl vinyl ether copolymer, atetrafluoroethylene/hexafluoropropylene copolymer or anethylene/tetrafluoroethylene copolymer.

The resin other than the fluorinated copolymer (a) is preferably afluorinated copolymer (excluding the fluorinated copolymer (a)) from theviewpoint of the electrical reliability. In such a case, when such afluorinated copolymer has a melting point of at least 280° C. and atmost 320° C., excellent heat resistance will be achieved, and swelling(foaming) of the fluorinated resin layer due to heat tends to besuppressed when the after-described printed circuit board is subjectedto solder reflow at high temperature or a soldering iron at hightemperature is pressed against the printed circuit board.

The composition containing the fluorinated copolymer (a) preferablycontains no resin other than the fluorinated copolymer, with a view tomaintaining excellent electrical properties of the fluorinated resinlayer, such as a low dielectric constant or low dielectric loss tangent.

The composition containing the fluorinated copolymer (a) may contain anadditive within a range not to impair the effects of the presentinvention as the case requires.

The additive is preferably an inorganic filler having a low dielectricconstant and low dielectric loss tangent. As such an inorganic filler,silica, clay, talc, calcium carbonate, mica, diatomaceous earth,alumina, zinc oxide, titanium oxide, calcium oxide, magnesium oxide,iron oxide, tin oxide, antimony oxide, calcium hydroxide, magnesiumhydroxide, aluminum hydroxide, basic magnesium carbonate, magnesiumcarbonate, zinc carbonate, barium carbonate, dawsonite, hydrotalcite,calcium sulfate, barium sulfate, calcium silicate, montmorillonite,bentonite, activated clay, sepiolite, imogolite, sericite, glass fiber,glass beads, silica-based balloons, carbon black, carbon nanotubes,carbon nanohom, graphite, carbon fibers, glass balloons, carbon burn,wood flour, zinc borate, etc. may be mentioned. Such inorganic fillersmay be used alone, or two or more of them may be used in combination.

The inorganic filler may be porous or non-porous. It is preferablyporous in that the dielectric constant or dielectric loss tangent isthereby further low.

The inorganic filler may be surface-treated with a surface treatmentagent such as a silane coupling agent or a titanate coupling agent inorder to improve the dispersibility in the fluorinated copolymer (a).

In a case where an inorganic filler is incorporated, the content of theInorganic filler is preferably from 0.1 to 100 parts by mass, morepreferably from 0.1 to 60 parts by mass, to 100 parts by mass of thefluorinated copolymer (a).

The thickness of the fluorinated resin layer is preferably from 1 to 200μm in the adhesive film (A2). In a case where the film is used for aflexible printed circuit board for which flexibility is required, it ispreferably from 1 to 50 μm. From the viewpoint of the resistance to asoldering iron at high temperature, it is preferably from 1 to 20 μm,more preferably from 3 to 20 μm, particularly preferably from 3 to 15μm. The thickness of the fluorinated resin layer is preferably from 3 to3,000 μm, more preferably from 3 to 500 μm, particularly preferably from5 to 300 μm in the case of the film (A1).

When the thickness of the fluorinated resin layer is at most the upperlimit value of the above range, the thicknesses of the after-describedprinted circuit board material, metal laminate and printed circuit boardcan be made thin. When it is at most the upper limit value of the aboverange, the fluorinated resin layer will be excellent in heat resistance,and swelling (foaming) of the fluorinated resin layer due to heat tendsto be suppressed when the after-described printed circuit board issubjected to solder reflow at high temperature or a soldering iron athigh temperature is pressed against the printed circuit board. When thethickness of the fluorinated resin layer is at least the lower limitvalue of the above range, excellent electrical insulating propertieswill be achieved.

In a case where the fluorinated resin layer is provided on both side ofthe heat resistant resin film, the thickness of the fluorinated resinlayer is the thickness on one side, not the total thickness on bothsides.

In this specification, the thickness of a film or layer may be measurede.g. by a micrometer.

The fluorinated resin layer may be laminated only on one side of theheat resistant resin film, or may be laminated on both sides. With aview to suppressing warpage of the adhesive film or obtaining adouble-sided metal laminate having excellent electrical reliability, itis preferred that the fluorinated resin layer is laminated on both sidesof the heat resistant resin film.

In a case where the fluorinated resin layer is laminated on both sidesof the heat resistant resin film, the composition (the type of thefluorinated copolymer (a), the type and the content of the optionalcomponent, etc.) and the thickness of the respective fluorinated resinlayers may be the same or different. With a view to suppressing warpageof the adhesive film (A2), it is preferred that the composition and thethickness of the respective fluorinated resin layers are the same.

<Heat Resistant Resin Film>

The heat resistant resin film is a film comprising one or more heatresistant resins, and may be a single layered film or a multilayeredfilm. However, the heat resistant resin film contains no fluorinatedpolymer.

In this specification, the heat resistant resin means a polymericcompound having a melting point of at least 280° C., or a polymericcompound having a highest continuous use temperature of at least 121° C.as defined in JIS C4003: 2010 (IEC 60085:2007).

As the heat resistant resin, for example, polyimide (aromatic polyimide,etc.), polyarylate, polysulfone, polyallyl sulfone (polyethersulfone,etc.), aromatic polyamide, aromatic polyether amide, polyphenylenesulfide, polyallyl ether ketone, polyamide imide, liquid crystalpolyester, etc. may be mentioned.

The heat resistant resin film may be produced, for example, by a methodof forming a heat resistant resin or a resin composition containing aheat resistant resin by a known forming method (such as casting,extrusion or blown-film extrusion). As the heat resistant resin film, acommercial product may be used. The surface of the heat resistant resinfilm, for example, the surface to be laminated with a fluororesin layer,may be subjected to surface treatment. The method for such surfacetreatment is not particularly limited, and may suitably be selected foruse from among known methods such as corona discharge treatment, plasmatreatment, etc.

As the heat resistant resin film, a polyimide film is preferred. Apolyimide film is a film composed of a polyimide. The polyimide film maycontain an additive, as the case requires, within a range not to impairthe effects of the present invention.

The polyimide constituting the polyimide film is not particularlylimited. It may be either a polyimide having no thermoplasticity or athermoplastic polyimide. The polyimide may, for example, be preferablyan aromatic polyimide. Particularly preferred is a wholly aromaticpolyimide produced by condensation polymerization of an aromaticpolyvalent carboxylic acid dianhydride and an aromatic diamine.

The polyimide is usually obtained by a reaction (polycondensation) of apolyvalent carboxylic acid dianhydride (or its derivative) and a diaminevia a polyamic acid (polyimide precursor).

A polyimide, particularly an aromatic polyimide, is insoluble in asolvent or the like due to its rigid main chain structure and isinfusible. Accordingly, first, by the reaction of a polyvalentcarboxylic acid dianhydride and a diamine, a polyimide precursor(polyamic acid or a polyamide acid) soluble in an organic solvent isprepared, and forming is conducted by various methods at this polyamicacid stage. Then, the polyamic acid is dehydrated by heating or by achemical method and cyclized (imidized) to obtain a polyimide.

As specific examples of the aromatic polyvalent carboxylic aciddianhydride, for example, ones disclosed in JP-A-2012-145676, paragraph[0055] may be mentioned.

As specific examples of the aromatic diamine, for example, onesdisclosed in JP-A-2012-145676, paragraph [0057] may be mentioned.

The additive which the polyimide film may contain is preferably aninorganic filler having a low dielectric constant or low dielectric losstangent. As such an inorganic filler, fillers mentioned for thecomposition containing the fluorinated copolymer (a) may be mentioned.Such inorganic fillers may be used alone, or two or more of them may beused in combination.

The inorganic filler may be porous or non-porous. It is preferablyporous in that the dielectric constant or dielectric loss tangent isthereby further low.

The inorganic filler may be surface-treated with a surface treatmentagent such as a silane coupling agent or a titanate coupling agent inorder to improve the dispersability in the polyimide.

In a case where an inorganic filler is contained, the content of theinorganic filler in the polyimide film is preferably from 0.1 to 100mass %, more preferably from 0.1 to 60 mass %, based on the polyimide.

The thickness of the heat resistant resin film is preferably from 3 to2,500 μm, and in a case where the film is used for a flexible printedcircuit board for which flexibility is required, it is preferably from 3to 50 μm, more preferably from 5 to 25 μm, particularly preferably from6 to 25 μm. When the thickness of the heat resistant resin film is atleast the lower limit value of the above range, excellent electricalinsulating property will be achieved, and when it is at most the upperlimit value of the above range, the total thickness of the adhesive film(A2) can be made thin.

In the adhesive film (A2), the thickness of the heat resistant resinfilm is preferably thicker than the thickness of the fluorinated resinlayer. That is, the thickness of the fluorinated resin layer ispreferably thinner than the thickness of the heat resistant resin film,whereby swelling (foaming) of the fluorinated resin layer due to heatcan be more effectively suppressed when the after-described printedcircuit board is subjected to solder reflow at high temperature or asoldering iron at high temperature is pressed against the printedcircuit board.

The thickness of the heat resistant resin film is preferably more thanone time, more preferably at least 1.25 times and at most 25 times,particularly preferably at least 1.66 times and at most 8.3 times thethickness of the fluorinated resin layer.

<Thickness of and Method for Producing Film (A1)>

The thickness of the film (A1) is the thickness of the fluorinated resinlayer, and is preferably within the above range. The film (A1) may beproduced by a conventional method. For example, the fluorinatedcopolymer (a) as it is or a resin composition obtained by kneading thefluorinated copolymer (a) and another component used as the caserequires, is formed into a film by a known forming method such asextrusion or blown-film extrusion, thereby to obtain a fluorinated resinfilm.

<Thickness of and Method for Producing Adhesive Film (A2)>

The entire thickness of the adhesive film (A2) is preferably at most3,000 μm, and is preferably at most 100 μm in a case where the film isused for a flexible printed circuit board for which flexibility isrequired. Particularly to applications for which high flexibility isrequired, it is preferably from 5 to 50 μm. The thinner the entirethickness of the adhesive film (A2), the more the flexibility improves,and the lighter the mass per unit area.

The adhesive film (A2) may be produced by laminating the fluorinatedresin layer on one side or on both sides of the heat resistant resinfilm. The fluorinated resin layer has adhesion due to the functionalgroup (i). Accordingly, the fluorinated resin layer can be directlylaminated on the heat resistant resin film without using an adhesive.

The method of laminating the fluorinated resin layer is not particularlylimited so long as the heat resistant resin film and the fluorinatedresin layer can be directly laminated, however a heat lamination methodor an extrusion lamination method is preferred with a view to improvingthe electrical properties and the heat resistance of the adhesive film(A2).

By heat lamination method, a preliminarily formed fluorinated resin filmand a heat resistant resin film are overlaid and hot-pressed to laminatethese films.

By extrusion lamination method, the fluorinated copolymer (a) or acomposition containing it is melted and extruded into a film, which islaminated on the heat resistant resin film.

Forming of the fluorinated resin film may be carried out by the aboveconventional method.

The surface of the fluorinated resin film, for example, the surface tobe laminated on the heat resistant resin film, may be surface-treated.The surface treatment method is not particularly limited and may beproperly selected from among known surface treatment methods such ascorona discharge treatment and plasma treatment.

As the hot press conditions in the heat lamination method, thetemperature is preferably from 295 to 420° C., more preferably from 300to 400° C. The pressure is preferably from 0.3 to 30 MPa, morepreferably from 0.5 to 20 MPa, most preferably from 1 to 10 MPa. Thetime is preferably from 3 to 240 minutes, more preferably from to 120minutes, most preferably from 10 to 80 minutes. The hot press may becarried out by using a pressing plate or a roll. The pressing plate ispreferably a stainless steel plate.

(Step (I))

The step (I) is a step of subjecting the film (A) to a heat treatment toobtain a material for a printed circuit board.

In the step (I), the heat treatment is carried out so that the ratio ofMFR (II) to MRF (I) [MFR (II)/MFR (I)] is from 0.05 to 0.5 and that MFR(II) is at most 15 g/10 min, where MFR (I) is MFR of the fluorinatedresin layer of the film (A) before the heat treatment, and MFR (II) isMFR of the fluorinated resin layer after the heat treatment. Further,the heat treatment temperature is a temperature of at least 250° C. andlower by at least 5° C. than the melting point of the fluorinatedcopolymer (a).

A printed circuit board formed of such a material for a printed circuitboard obtained by subjecting the film (A) to a heat treatment, is lesslikely to be deformed and is hardly warped at the time of solder reflowat high temperature or when a soldering iron at high temperature ispressed against the printed circuit board. The reason is considered tobe as follows. That is, by subjecting the film (A) to a heat treatment,the rigidity of the fluorinated resin layer of the film (A) improves,and the linear expansion coefficient of the fluorinated resin layerdecreases. As a result, the difference in the linear expansioncoefficient between the fluorinated resin layer and the after-describedmetal layer in the printed circuit board is reduced, and deformationsuch as warpage particularly in a high temperature region (from 150 to200° C.) decreases. Further, it is also found that the storage elasticmodulus of the fluorinated resin layer of the film (A) also tends toimprove. The storage elastic modulus is an index for the rigidity, and afluorinated resin layer having a high storage elastic modulus isconsidered to be less likely to have deformation such as warpage.

Further, in recent years, use of the printed circuit board in anenvironment at a temperature higher than 150° C. is sometimes assumed.For example, WO2011/077917 discloses that a flexible printed circuitboard used for an on-vehicle electronic device is repeatedly exposed tohigh temperature environment of about 150° C. Further, a device otherthan an on-vehicle electronic device, for example, a notebook personalcomputer or a super computer having a CPU (Central Processing Unit)capable of high speed treatment, employs a flexible printed circuitboard for further downsizing and weight reduction. In such a devicealso, by heat generated from the CPU, the flexible printed circuit boardis repeatedly exposed to high temperature environment. Whereas, bysubjecting the film (A) to a heat treatment as described above, thelinear expansion coefficient of the fluorinated resin layer in the film(A) is decreased, and the difference in the linear expansion coefficientbetween the fluorinated resin layer and the after-described metal layercan be reduced. Accordingly, even when the printed circuit board is usedfor such an application, deformation such as warpage of the printedcircuit board due to a difference in the linear expansion coefficientbetween the fluorinated resin layer and the metal layer can besuppressed.

In the step (I), the heat treatment is carried out so that [MFR (II)/MFR(I)] is preferably from 0.05 to 0.4, more preferably from 0.05 to 0.35,particularly preferably from 0.1 to 0.3. When [MFR (II)/MFR (I)] iswithin the above range, the heat treatment may be moderately carriedout, and the linear expansion coefficient of the fluorinated resin layercan be sufficiently decreased. Further, the storage elastic modulus ofthe fluorinated resin layer tends to further increase. When [MFR(II)/MFR (I)] is higher than the upper limit value of the above range,the heat treatment may be insufficient, and if it is less than the lowerlimit value of the above range, heat deterioration (e.g. decompositionof the fluorinated resin layer) will proceed.

In the step (I), the heat treatment is carried out so that MFR (II)satisfies preferably at most 15 g/10 min, more preferably at most 10g/10 min, particularly preferably at most 5 g/10 min. When MFR (II) isat most the upper limit value of the above range, the linear expansioncoefficient of the fluorinated resin layer will be sufficientlydecreased.

Further, in the step (I), the heat treatment is carried out so that MFR(II) satisfies preferably at least 0.5 g/10 min, more preferably atleast 1 g/10 min, particularly preferably at least 1.5 g/10 min. WhenMFR (II) is at least the above lower limit value, excellentprocessability will be achieved when the metal layer is directlylaminated on the fluorinated resin layer in the after-described step(II).

In a case where the film (A) is the film (A1), the storage elasticmodulus of the obtained material for a printed circuit board (that is,the film (A1) after the heat treatment) is preferably at least 650 MPa,more preferably at least 800 MPa, particularly preferably at least 900MPa. Further, the storage elastic modulus is preferably at most 5,000MPa, more preferably at most 2.000 MPa, particularly preferably at most1,500 MPa. When the storage elastic modulus is at least the above lowerlimit value, the rigidity of the material for a printed circuit boardwill be more excellent, and the linear expansion coefficient tends tofurther decrease. When the storage elastic modulus is at most the aboveupper limit value, such is useful for application to a flexible printedcircuit board for which flexibility is required.

In the material for a printed circuit board thus produced, thefunctional groups (i) contained in the fluorinated resin layer arereduced via the heat treatment in the step (I) but remain.

That is, the produced material for a printed circuit board (fluorinatedresin layer) comprises a composition containing the fluorinatedcopolymer having the functional group (i) and has a melt flow rate of atmost 15 g/10 min measured at 372° C. under a load of 49 N. Further, thestorage elastic modulus of the fluorinated resin layer in the producedmaterial for a printed circuit board is usually at least 650 MPa by theheat treatment, preferably at least 800 MPa, more preferably at least900 MPa.

In this specification, the storage elastic modulus is a storage elasticmodulus measured by using a dynamic viscoelasticity apparatus “DMS6100”(manufactured by Seiko Instruments Inc.) at a temperature-increasingrate of 2° C./min at tensile mode under a frequency of 1 Hz at 23° C.

In a case where the film (A) is the above-described adhesive film (A2),the linear expansion coefficient of the obtained material for a printedcircuit board (that is, the adhesive film (A2) after the heat treatment)at from 150 to 200° C. is preferably from 0 to 25 ppm/° C., morepreferably from 10 to 23 ppm/° C. When the linear expansion coefficientat a high temperature region is at most the above upper limit value, theabove-described deformation such as warpage can be further decreased.Further, a material for a printed circuit board having a linearexpansion coefficient of at least the above lower limit value willreadily be obtained by the above heat treatment.

In the material for a printed circuit board thus produced, thefunctional groups (i) contained in the fluorinated resin layer arereduced via the heat treatment in the step (I) but remain.

That is, the fluorinated resin layer in the produced material for aprinted circuit board (a laminate of the heat resistant resin film andthe fluorinated resin layer) comprises a composition containing thefluorinated copolymer having the functional group (i) and has a meltflow rate of at most 15 g/10 min measured at 372° C. under a load of 49N. Further, the linear expansion coefficient of the produced materialfor a printed circuit board at from 150 to 200° C. is usually from 0 to25 ppm/° C. by the heat treatment, preferably from 10 to 23 ppm/° C.

In this specification, the linear expansion coefficient is a valuemeasured by a thermo-mechanical analyzer manufactured by S1Nanotechnology Inc. (TMA/SS6100) with respect to a sample cut in a stripform of 4 mm×50 mm and dried in an oven at 250° C. for 2 hours forconditioning. Specifically, the sample is heated at a rate of 5° C./minfrom 30° C. to 250° C. while a load of 2.5 g is applied in the airatmosphere with a distance between chucks of 20 mm, and a change due tolinear expansion of the sample is measured. After completion of themeasurement, in a case where the linear expansion coefficient at from150 to 200° C. is to be obtained, the linear expansion coefficient(ppm/C) at from 150 to 200° C. is obtained from a change of the sampleat from 150 to 200° C.

[MFR (II)/MFR (I)] and MFR (I) may be controlled e.g. by a method ofadjusting the heat treatment temperature in the step (I), a method ofadjusting the heat treatment time, or a combination thereof.

The heat treatment temperature is a temperature of at least 250° C. andlower by at least 5° C. than the melting point of the fluorinatedcopolymer (a) and is a temperature so that [MFR (II)/MFR (I)] and MFR(II) are within the above ranges, and is preferably a temperature of atleast 260° C. and lower by at least 5° C. than the melting point of thefluorinated copolymer (a). When the heat treatment temperature is atleast the lower limit value of the above range, the heat treatment canbe conducted in a short time, thus leading to excellent productivity ofthe material for a printed circuit board. When it is at most the upperlimit value of the above range, heat deterioration (e.g. decompositionof the fluorinated resin layer) of the material for a printed circuitboard can be suppressed.

The heat treatment time is preferably for example from 1 to 360 hours,more preferably from 3 to 336 hours, particularly preferably from 6 to192 hours.

The heat treatment equipment is not particularly limited and may, forexample, be a circulating hot air dryer, a wicket dryer, a tunnel dryeror an infrared dryer.

(Step (I))

The step (II) is a step of directly laminating a metal layer on thefluorinated resin layer of the film (A1) or the adhesive film (A2) ofthe material for a printed circuit board obtained in the step (I) toobtain a metal laminate. The fluorinated resin layer has adhesionderived from the functional group (I). Accordingly, the metal layer canbe directly laminated on the fluorinated resin layer without using anadhesive.

In a case where the material for a printed circuit board is producedfrom the adhesive film (A2) and has the heat resistant resin film andthe fluorinated resin layer laminated on both sides of the heatresistant resin film, the metal layer may be laminated on one of thefluorinated resin layers or may be laminated on both the fluorinatedresin layers.

The metal layer is not particularly limited and may be properly selecteddepending upon the application. In a case where the after-describedprinted circuit board is used for electronic equipment or electricalapparatus for example, the metal layer may, for example, be a metal foilof copper or a copper alloy, stainless steel or its alloy, nickel or anickel alloy (including 42 alloy), aluminum or an aluminum alloy. For aconventional printed circuit board commonly used in such applications, acopper foil such as a rolled copper foil or an electrolytic copper foilis widely used as the metal layer and may be preferably used also in thepresent invention.

On the surface of the metal layer, an anticorrosive layer (for example,an oxide coating film of e.g. chromate) or a heat resistant layer may beformed. Further, for the purpose of improving the adhesion to thefluorinated resin layer, a treatment with a coupling agent may beapplied to the surface of the metal layer.

The thickness of the metal layer is not particularly limited so long asa sufficient function can be exhibited depending upon the application ofthe printed circuit board.

The metal laminate may be produced by bonding and directly laminating ametal foil for forming the metal layer on the fluorinated resin layer.

Bonding of the fluorinated resin layer and the metal foil may beconducted by a known method. For example, the fluorinated resin layerand the metal foil may be bonded by continuous treatment by a heatedroller laminator having at least one pair of metal rollers or a doublebelt press (DBP). In view of simple apparatus constitution andadvantages in the maintenance cost, bonding of the fluorinated resinlayer and the metal foil is carried out preferably by heat laminationusing a heated roller laminator having at least one pair of metalrollers.

The “heated roller laminator having at least one pair of metal rollers”is an apparatus having metal rollers for heating and pressurizing thematerial, and its specific apparatus structure is not particularlylimited.

The specific structure of a means to conduct the heat lamination is notparticularly limited, however, to achieve a favorable appearance of theobtainable metal laminate, it is preferred to dispose a protectivematerial between the surface to be pressurized and the metal foil.

The protective material is not particularly limited so long as itwithstands the heating temperature in the heat lamination step, and ispreferably a heat resistant plastic film of e.g. a non-thermoplasticpolyimide or a metal foil such as a copper foil, an aluminum foil or aSUS foil. Particularly, a non-thermoplastic polyimide film is morepreferred in view of excellent balance between the heat resistance, therecyclability, etc. Further, the thickness of the non-thermoplasticpolyimide film is preferably at least 75 μm, since if it is too thin,the protective material may not sufficiently fulfill the role as abuffer and a protector at the time of lamination. The protectivematerial is not necessarily a single layer and may have a multilayerstructure of two or more layers differing in the properties.

The method of heating the materials to be laminated (that is, the film(A1) or the adhesive film (A2) and the metal foil for forming the metallayer) in the above heat lamination means is not particularly limited,and for example, a known heating means capable of heating at apredetermined temperature, such as a circulating hot air method, a hotair heating method or an induction heating method may be employed.Likewise, the method of pressurizing the materials to be laminated inthe heat lamination means is not particularly limited, and for example,a known pressurizing means capable of applying predetermined pressure,such as a hydraulic method, a pneumatic method or a pressurizationmethod between gaps may be employed.

The heating temperature in the heat lamination step, that is, thelamination temperature, is preferably a temperature of the glasstransition temperature (Tg) of the fluorinated resin layer+50° C. orhigher, more preferably Tg of the fluorinated resin layer+100° C. orhigher. When it is a temperature of Tg+50° C. or higher, the fluorinatedresin layer and the metal layer may be favorably heat-laminated.Further, when it is a temperature of Tg+100° C. or higher, thelamination rate may be increased, thus further improving theproductivity.

Tg of the fluorinated resin layer means Tg of the resin constituting thefluorinated resin layer (that is, the fluorinated copolymer (a) or acomposition containing the fluorinated copolymer (a)).

Further, the lamination temperature is preferably at most 420° C., morepreferably at most 400° C. The fluorinated resin layer formed on one ofor both sides of the heat resistant resin film of the adhesive film (A2)has adhesion to the metal layer. Accordingly, the heat lamination can becarried out at low temperature. Therefore, it is possible to suppressdimensional changes which occur when wirings are formed by etching orsolder reflow is conducted for mounting the members, due to residualstrain formed on the metal laminate by the high temperature during theheat lamination.

The lamination rate in the heat lamination step is preferably at least0.5 m/min, more preferably at least 1.0 m/min. When it is at least 0.5m/min, sufficient heat lamination can be carried out, and when it is atleast 1.0 m/min, the productivity will further improve.

The higher the pressure in the heat lamination step, that is, thelamination pressure, the lower the lamination temperature can be made,and the higher the lamination rate can be made. However, if thelamination pressure is too high, usually the dimensional changes of theobtainable metal laminate tend to be significant. Further, on thecontrary, if the lamination pressure is too low, the adhesive strengthof the metal layer of the obtainable metal laminate tends to be low.Accordingly, the lamination pressure is preferably within a range offrom 49 to 490 N/cm (from 5 to 50 kgf/cm), more preferably from 98 to294 N/cm (from 10 to 30 kgf/cm). Within such a range, three conditionsi.e. the lamination temperature, the lamination rate and the laminationpressure will be favorable, and the productivity will further improve.

The tensile force of the film (A) in the lamination step is preferablyfrom 0.01 to 4 N/cm, more preferably from 0.02 to 2.5 N/cm, particularlypreferably from 0.05 to 1.5 N/cm. If the tensile force is lower than theabove range, sagging or meandering may occur during transport of thelaminate, and the laminate may not be uniformly fed into the heatedrollers, whereby a metal laminate with a favorable appearance may hardlybe obtained. On the other hand, if the tensile force is higher than theabove range, the influence of the tensile force tends to be significant,and the dimensional stability may be deteriorated.

In the step (II), it is preferred to use a heat lamination apparatus ofcontinuously heating and pressure-bonding the materials to be laminated,such as the heated roller laminate or having at least one pair of metalrollers. In such a heat lamination apparatus, at a stage prior to theheat lamination means (e.g. at least one pair of metal rollers), amaterial supplying means of supplying the materials to be laminated maybe provided, or at a stage after the heat lamination means, a materialwinding means of winding the materials to be laminated may be provided.By such means, the productivity of the heat lamination apparatus willfurther improve. Specific structures of the material supplying means andthe material winding means are not particularly limited, and forexample, a known roll winding machine capable of winding the film (A) orthe metal layer, or the obtainable metal laminate may, for example, bementioned.

Further, it is more preferred to provide a protective material windingmeans or a protective material supplying means of winding or supplyingthe protective material. When such a protective material winding meansor a protective material supplying means is provided, the protectivematerial once used in the heat lamination step can be wound and suppliedagain and can thereby be recycled. Further, in order to arrange the bothends of the protective material when wound, an end position detectingmeans and a winding position correcting means may be provided. By suchmeans, the protective material can be wound while the ends of theprotective material can be arranged precisely, whereby the recycleefficiency can be improved. Specific structures of such a protectivematerial winding means, a protective material supplying means, an endposition detecting means and a winding position correcting means are notparticularly limited, and known apparatus may be used.

(Step (III))

The step (III) is a step of etching the metal layer of the metallaminate obtained in the step (II) to form a patterned circuit to obtaina printed circuit board.

The etching may be carried out, for example, by a conventional methodsuch as chemical etching (wet etching) of using an etching liquid suchas an acidic solution such as a copper chloride solution or nitric acid;or an alkali solution.

The obtained printed substrate may be used as a flexible printed circuitboard when a flexible film (A) is used.

(Step (IV))

The step (IV) is a step of soldering the patterned circuit of theprinted circuit board obtained in the step (II) using a soldering iron.

The step (IV) may be a step of placing only solder for example in aspherical form on the patterned circuit, or may be a step of mountinge.g. an electronic member together with solder.

The printed circuit board obtained in the step (III) is one produced viathe above step (I), and the fluorinated resin layer in the printedcircuit board has a low linear expansion coefficient. Accordingly, evenwhen a soldering iron at high temperature is pressed against the printedcircuit board in the step (IV), the printed circuit board is less likelyto be warped.

Second Embodiment

According to a second embodiment of the present invention, the presentinvention provides a method for producing a metal laminate, whichcomprises subjecting a metal laminate precursor to a heat treatment toobtain a metal laminate.

The metal laminate precursor is a laminate having the adhesive film (A2)described in the first embodiment and a metal layer directly laminatedon at least one fluorinated resin layer of the adhesive film (A2).

In the second embodiment, the heat treatment is carried out at atemperature of at least 250° C. and lower by at least 5° C. than themelting point of the fluorinated copolymer (a) so that the ratio of MFR(VI) to MFR (V) [MFR (VI)/MFR (V)] is from 0.05 to 0.5 and that MFR (VI)is at most 15 g/10 min, where MFR (V) is MFR of the fluorinated resinlayer before the heat treatment, and MFR (VI) is MFR of the fluorinatedresin layer after the heat treatment.

The production method according to the second embodiment may comprise,after the metal laminate is produced by a step of subjecting the metallaminate precursor to a heat treatment (hereinafter sometimes referredto as step (V)), a step of etching the metal layer of the metal laminateto form a patterned circuit thereby to produce a printed circuit board(hereinafter sometimes referred to as step (VI)) and a step of solderingthe formed patterned circuit by a soldering iron (hereinafter sometimesreferred to as a step (VII)).

(Metal Laminate Precursor)

The metal laminate precursor is a plate comprising the adhesive film(A2) and a metal layer directly laminated on at least one fluorinatedresin layer of the adhesive film (A2).

The structure, the production method, etc. of the adhesive film (A2) areas described in the first embodiment.

The structure, etc. of the metal layer are as described in the step (II)in the first embodiment.

In production of the metal laminate precursor, a specific method ofdirectly laminating a metal layer on at least one fluorinated resinlayer of the adhesive film (A2), as described in the step (II) in thefirst embodiment, a known bonding means using, for example, a heatedroller laminator having at least one pair of metal rollers or a doublebelt press (DBP) may be mentioned. Further, in a case where the adhesivefilm (A2) has a fluorinated resin layer on both sides thereof, the metallayer may be laminated on one of the fluorinated resin layers or may belaminated on both the fluorinated resin layers.

(Step (V))

The step (V) is a step of subjecting the metal laminate precursor to aheat treatment to obtain a metal laminate.

In the step (V), the heat treatment is carried out so that the ratio ofMFR (VI) to MFR (V) MFR (VI)/MFR (V) is from 0.05 to 0.5 and that MFR(VI) is at most 15 g/10 min, where MFR (V) is MFR of the fluorinatedresin layer which the metal laminate precursor before the heat treatmenthas, and MFR (VI) is MFR of the fluorinated resin layer after the heattreatment. Further, the heat treatment temperature is a temperature ofat least 250° C. and lower by at least 5° C. than the melting point ofthe fluorinated copolymer (a).

Such a printed circuit board provided with a metal laminate obtained bysubjecting the metal laminate precursor to a heat treatment is lesslikely to be deformed and is hardly warped, at the time of solder reflowat high temperature or when a soldering iron at high temperature ispressed against the printed circuit board. The reason is considered tobe as follows. That is, by subjecting the metal laminate precursor to aheat treatment, the rigidity of the fluorinated resin layer of theadhesive film (A2) constituting the metal laminate precursor improves,and the linear expansion coefficient of the fluorinated resin layerdecreases. As a result, in the printed circuit board, the difference inthe linear expansion coefficient between the fluorinated resin layer andthe metal layer is reduced, and deformation such as warpage particularlyin a high temperature region (from 150 to 200° C.) decreases. Further,it was further found that by the heat treatment, the storage elasticmodulus of the fluorinated resin layer of the adhesive film (A2) alsotends to improve. The storage elastic modulus is an index for therigidity as described above, and a fluorinated resin layer having a highstorage elastic modulus is considered to be less likely to havedeformation such as warpage.

Further, as described above, in recent years, use of the printed circuitboard in an environment at a temperature higher than 150° C. issometimes assumed. By subjecting the metal laminate precursor to a heattreatment as described above, the linear expansion coefficient of thefluorinated resin layer of the adhesive film (A2) constituting the metallaminate precursor can be decreased, and the difference in the linearexpansion coefficient between the fluorinated resin layer and the metallayer can be reduced. Accordingly, even when a printed circuit board isused for such applications, as described above, deformation such aswarpage of a printed circuit board due to a difference in the linearexpansion coefficient between the fluorinated resin layer and the metallayer can be suppressed.

In the step (V), the heat treatment is carried out so that [MFR (VI)/MFR(V)] is preferably from 0.05 to 0.4, more preferably from 0.05 to 0.35,particularly preferably from 0.1 to 0.3. When [MFR (VI)/MFR (V)] iswithin the above range, the heat treatment is moderately carried out,and the linear expansion coefficient of the fluorinated resin layer canbe sufficiently decreased. Further, the storage elastic modulus of thefluorinated resin layer tends to further increase. If [MFR (VI)/MFR (V)]exceeds the upper limit value of the above range, the heat treatmenttends to be insufficient, and if it is less than the lower limit valueof the above range, heat deterioration (such as decomposition of thefluorinated resin layer) will proceed.

In the step (V), the heat treatment is carried out so that MFR (VI) ispreferably at most 15 g/10 min, more preferably at most 10 g/10 min,particularly preferably at most 5 g/10 min. When MFR (VI) is at most theabove upper limit value, the linear expansion coefficient of thefluorinated resin layer will be sufficiently decreased.

Further, MFR (VI) may be 0 g/10 min by the heat treatment in the step(V)₁, however, the heat treatment is preferably carried out so that MFR(V) is at least 0.5 g/10 min, more preferably at least 1.0 g/10 min,particularly preferably at least 1.5 g/10 min, in that melt processingsuch as hot press is further carried out to prepare a multilayer circuitboard.

The linear expansion coefficient of the adhesive film in the obtainedmetal laminate at from 150 to 200° C. is preferably from 0 to 25 ppm/°C., more preferably from to 23 ppm/° C. When the linear expansioncoefficient in a high temperature region is at most the above upperlimit value, the warpage can be further suppressed. Further, a metallaminate having an adhesive film having a linear expansion coefficientof at least the above lower limit value will readily be obtained by theabove heat treatment.

In the metal laminate thus produced, the functional groups (i) containedin the fluorinated resin layer are reduced via the heat treatment in thestep (V) but remain. That is, the fluorinated resin layer in theproduced metal laminate (a laminate of the heat resistant resin film,the fluorinated resin layer and the metal layer) comprises a compositioncontaining a fluorinated copolymer having the functional group (i) andhas a melt flow rate of at most 15 g/10 min measured at 372° C. under aload of 49 N. Further, the linear expansion coefficient of the adhesivefilm (a laminate of the heat resistant resin film and the fluorinatedresin layer) in the produced metal laminate at from 150 to 200° C.becomes usually from 0 to 25 ppm/° C., preferably from 10 to 23 ppm/°C., by the heat treatment.

[MFR (VI)/MFR (V)] and MFR (VI) may be controlled e.g. by a method ofadjusting the heat treatment temperature in the step (V), a method ofadjusting the heat treatment time, or a combination thereof.

The heat treatment temperature is a temperature of at least 250° C. andlower by at least 5° C. than the melting point of the fluorinatedcopolymer (a) and is a temperature so that [MFR (VI)/MFR (V)] and MFR(VI) are within the above ranges, and is preferably a temperature of atleast 260° C. and lower by at least 5° C. than the melting point of thefluorinated copolymer (a). When the heat treatment temperature is atleast the lower limit value of the above range, the heat treatment canbe conducted in a short time, thus leading to an excellent productivityof the metal laminate. When it is at most the upper limit value of theabove range, heat deterioration (e.g. decomposition of the fluorinatedresin layer) of the metal laminate can be suppressed.

The heat treatment time is preferably from 1 to 360 hours for example,more preferably from 3 to 336 hours, particularly preferably from 6 to192 hours.

The heat treatment equipment is not particularly limited and may, forexample, be a circulating hot air dryer, a wicket dryer, a tunnel dryeror an infrared dryer.

(Step (VI) and Step (VII))

The step (VI) is a step of etching the metal layer of the metal laminateobtained in the step (V) to form a patterned circuit to obtain a printedcircuit board.

The step (VII) is a step of soldering the patterned circuit board of theprinted circuit board obtained in the step (VI) by using a solderingiron.

The step (VI) may be carried out in the same manner as the step (III) inthe first embodiment, and the step (VII) may be carried out in the samemanner as the step (IV) in the first embodiment.

The printed circuit board thus obtained may be used as a flexibleprinted circuit board when it is produced by using a flexible adhesivefilm (A2).

Advantageous Effects

In the first and second embodiments, the fluorinated resin layercontains the fluorinated copolymer (a) having a functional group (i) andis favorably attached to the heat resistant resin film and the metallayer. Accordingly, the fluorinated resin layer functions as an adhesivelayer and is capable of laminating the heat resistant resin film and themetal layer without using an adhesive such as a thermosetting adhesive.

Further, since the fluorinated resin layer is used as the adhesivelayer, excellent heat resistance, flexibility, electrical reliability,etc., are achieved as compared with a case where a thermosettingadhesive is used for the adhesive layer.

Further, the fluorinated copolymer (a) has low dielectric properties(such as a dielectric constant and a dielectric loss tangent) and isexcellent in the electrical properties as compared with a thermoplasticpolyimide. Accordingly, by the fluorinated resin layer containing thefluorinated copolymer (a) being directly laminated on the metal layer, aprinted circuit board having a high signal transmission rate and a lowtransmission loss can be obtained.

Further, in the first embodiment, the object to be heat-treated in thestep (I) is the film (A), and in the second embodiment, the object to beheat-treated in the step (V) is the metal laminate precursor, and boththe film (A) and the metal laminate precursor which are objects to beheat-treated have the fluorinated resin layer. It is considered thatsince the fluorinated resin layer contains the fluorinated copolymer (a)having a functional group (i), by heat-treating the object to beheat-treated, a crosslinked structure is formed between molecules and inthe molecules of the fluorinated copolymer (a), the decompositionreaction of the main chain of the fluorinated copolymer (a) andbrittleness of the fluorinated resin layer due to the decompositionreaction are suppressed. Accordingly, it is estimated that the linearexpansion coefficient of the material for a printed circuit board in ahigh temperature region in the first embodiment and the linear expansioncoefficient of the adhesive film (A2) which the metal laminate has in ahigh temperature region in the second embodiment are reduced. It isestimated that the crosslinked structure is formed as a result ofintramolecular and intermolecular covalent bonds formed by activeradicals generated from the functional group (i) by heat. If a layercontaining a fluorinated copolymer having no functional group (i) isheat-treated, a crosslinked structure is hardly formed. Accordingly, itis considered that the decomposition reaction of the main chain proceedsby priority over the crosslinking reaction, and the linear expansioncoefficient in a high temperature region is less likely to be reduced.

Further, in the first embodiment, the heat treatment (step (I)) iscarried out on the film (A) before the metal layer is laminated. In sucha case, even when the adhesive film (A2) comprising the heat resistantresin film is used as the film (A) and the heat resistant resin filmcontains moisture in a large amount due to its moisture absorptionproperty, the moisture will be smoothly removed from the heat resistantresin film and the fluorinated resin layer during the heat treatment(step (I)). Accordingly, an effect such that bubbling due to moisturehardly occurs at the time of solder reflow of the printed circuit boardat high temperature or when a soldering iron at high temperature ispressed against the printed circuit board.

Whereas in the second embodiment, the heat treatment (step (V)) iscarried out on the metal laminate precursor having the metal layerlaminated on the adhesive film (A2). In such a case, although the reasonis not clearly understood, the effect of reducing the linear expansioncoefficient in a high temperature region is higher than in a case wherethe heat treatment is conducted on the film (A2) before the metal layeris laminated as in the first embodiment.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples of the present invention, however, it should beunderstood that the present invention is by no means restricted thereto.

Ex. 1, 3, 5, 6, 7 to 13 are Examples of the present invention, and Ex.2, 4, 14 to 16 are Comparative Examples.

<Evaluation Methods>

Measurements, tests and evaluations were conducted by the followingmethods.

(1) Copolymer Composition

The copolymer composition of the fluorinated copolymer (a) wascalculated from data measured by molten NMR analysis, fluorine contentanalysis and infrared absorption spectrum analysis.

(2) Content of Functional Group (i)

The proportion of constituting units based on NAH having a functionalgroup (i) in the fluorinated copolymer (a) was obtained as follows.

The fluorinated copolymer (a) was pressed to obtain a film having athickness of 200 μm. In the infrared absorption spectrum, the absorptionpeak of the constituting unit based on NAH in the fluorinated copolymerappears at 1,778 cm⁻¹ in each case. By measuring the absorbance of theabsorption peak, and using the molar extinction coefficient of NAH being20,810 mol⁻¹·l·cm⁻¹, the proportion (mol %) of the constituting unitsbased on NAH was obtained.

The number of the reactive functional groups (acid anhydride residues)per 1×10⁶ carbon atoms in the main chain is calculated to be [a×10⁶/100]groups, where a (mol %) is the above proportion.

(3) Melting Point

Using a differential scanning calorimeter (manufactured by SeikoInstruments & Electronics Ltd., DSC apparatus), the melting peak at thetime of heating the fluorinated copolymer (a) at a rate of 10° C./minwas recorded, and the temperature (° C.) corresponding to the maximumvalue was taken as the melting point.

(4) MFR

Using a melt indexer (manufactured by TECHNOL SEVEN CO., LTD.), the mass(g) of the fluorinated copolymer (a) flowing out from a nozzle with adiameter of 2 mm and a length of 8 mm in 10 minutes (unit time) at 372°C. under a load of 49 N, was measured.

(5) Linear Expansion Coefficient (Ppm/° C.)

A sample cut into a strip of 4 mm×55 mm was dried in an oven at 250° C.for 2 hours for conditioning, followed by measurement using athermo-mechanical analyzer (manufactured by SII Nanotechnology Inc.,TMA/SS6100). Specifically, the sample was heated from 30° C. to 250° C.at a rate of 5° C./min in the air with a distance between chucks of 20mm while a load of 2.5 g was applied, and a change due to linearexpansion of the sample was measured. After the measurement, the linearexpansion coefficient at from 50 to 100° C. was obtained from a changeof the sample from 50° C. to 100° C., the linear expansion coefficientat from 100 to 150° C. was obtained from a change of the sample from100° C. to 150° C., and the linear expansion coefficient at from 150 to200° C. was obtained from a change of the sample from 150° C. to 200° C.

(6) Relative Dielectric Constant

With respect to each of adhesive films in Ex. 3 and 4 describedhereinafter, the relative dielectric constants at frequencies of 2.5GHz, 10 GHz and 20 GHz were obtained by the split post dielectricresonator method (SPDR method) at 23° C. under 50% RH. Equipment used inthe measurement were nominal fundamental frequency of 2.5 GHz type splitpost dielectric resonator manufactured by QWED Company, vector networkanalyzer E8361C manufactured by Keysite Technologies and 85071E option300 relative dielectric constant calculation software manufactured byKeysite Technologies.

(7) Storage Elastic Modulus

Using a dynamic viscoelasticity apparatus (manufactured by SeikoInstruments Inc., DMS6100), the temperature was Increased at 2° C./minat tensile mode at a frequency of 1 Hz, and the storage elastic modulusat 23° C. was measured.

Production Example 1

A fluorinated copolymer (a-1) was produced as follows using NAH(anhydrous high-mix acid, manufactured by Hitachi Chemical Co., Ltd.) asa monomer to form the constituting units (m2) and PPVE (CF₂═CFO(CF₂)₃F,perfluoropropyl vinyl ether manufactured by Asahi Glass Company,Limited) as a monomer to form the constituting units (m3).

First, 369 kg of 1,3-dichloro-1,1,2,2,3-pentafluoropropane (“AK225cb”manufactured by Asahi Glass Company, Limited) and 30 kg of PPVE werecharged into a preliminarily degassed polymerization vessel having aninternal capacity of 430 L and equipped with a stirrer. Then, inside ofthe polymerization vessel was heated to raise the temperature to 50° C.,and 50 kg of TFE was further changed, whereupon the pressure in thepolymerization vessel was raised to 0.89 MPa/G.

Further, a polymerization initiator solution was prepared by dissolving(perfluorobutyryl) peroxide at a concentration of 0.36 mass % inAK225cb, and 3 L of the polymerization initiator solution wascontinuously added at a rate of 6.25 mL per minute into thepolymerization vessel, to carry out polymerization. Further, TFE wascontinuously charged in order to maintain the pressure in thepolymerization vessel during the polymerization reaction to be 0.89MPa/G. Further, a solution prepared by dissolving NAH at a concentrationof 0.3 mass % in AK225cb was charged continuously by an amountcorresponding to 0.1 mol % based on mols of TFE to be charged during thepolymerization.

After 8 hours from the initiation of polymerization, when 32 kg of TFEwas charged, the temperature in the polymerization vessel was lowered toroom temperature, and the pressure was purged to atmospheric pressure.The obtained slurry was separated from AK225cb by solid-liquidseparation and dried at 150° C. for 15 hours, to obtain 33 kg ofgranules of a fluorinated copolymer (a-1). The specific gravity of thefluorinated copolymer (a-1) was 2.15.

The composition of the fluorinated copolymer (a-1) was the constitutingunits based on TFE/the constituting units based on NAH/the constitutingunits based on PPVE=97.9/0.1/2.0 (mol %). The melting point of thefluorinated copolymer (a-1) was 300° C., and MFR was 17.2 g/10 min. Thecontent of the functional group (i) (acid anhydride group) in thefluorinated copolymer (a-1) was 1,000 groups per 1×10⁶ carbon atoms inthe main chain of the fluorinated copolymer (a-1).

Production Example 2

The granules of the fluorinated copolymer (a-1) were extruded at a dietemperature of 340° C. by means of a single screw extruder having adiameter of 30 mm and having a 750 mm width coat hanger die, to obtain afluororesin film having a thickness of 12.5 μm (hereinafter referred toas film (1)). With respect to the film (1), MFR (MFR (1)) was measuredand found to be 16.9 g/10 min.

Production Example 3

A fluororesin film (hereinafter referred to as film (A1-1) having athickness of 50 μm was obtained in the same manner as in ProductionExample 2 except that the winding rate was changed. With respect to thefilm (A1-1), MFR (MFR (I)) was measured and found to be 16.9 g/10 min.

Production Example 4

The film (1) and a polyimide film having a thickness of 25 μm(manufactured by Du Pont-Toray Co., Ltd., product name “Kapton 100EN”)were laminated in the order of film (1)/polyimide film/film (1) andpressed at a temperature of 360° C. under a pressure of 1.3 MPa for 10minutes to obtain an adhesive film (A2-1) having a three-layerstructure.

From the adhesive film (A2-1), one of the films (1) was separated, andMFR (1) of the film (1) was measured and found to be 16.7 g/10 min.

(Ex. 1)

The film (A1-1) obtained in Production Example 3 was heat-treated underconditions (temperature and time) as Identified in Table 1. MFR (II) andthe linear expansion coefficient of the film (A1-1) after the heattreatment were measured. The results are shown in Table 1.

Further, with respect to the film (A1-1) after the heat treatment,infrared absorption spectrum analysis was conducted, and it wasconfirmed that the acid anhydride residue derived from NAH remained.

(Ex. 2)

The linear expansion coefficient of the film (A1-1) obtained inProduction Example 3 without heat treatment was measured. The resultsare shown in Table 1. In the rows of MFR (1) and MFR (II) in Table 1,MFR of the film (A1-1) without heat treatment is shown for convenience.

(Ex. 3)

The adhesive film (A2-1) obtained in Production Example 4 washeat-treated under conditions (temperature and time) as identified inTable 1. The linear expansion coefficient and the relative dielectricconstant of the adhesive film (A2-1) after the heat treatment weremeasured. The results are shown in Table 1.

Further, from the adhesive film (A2-1) after the heat treatment, one ofthe films (1) was separated, and MFR (II) of the film (1) was measured.The results are shown in Table 1. Further, with respect to the separatedfilm (1), infrared absorption spectrum analysis was conducted, and itwas confirmed that the acid anhydride residue derived from NAH remained.

(Ex. 4)

The linear expansion coefficient and the relative dielectric constant ofthe adhesive film (A2-1) obtained in Production Example 4 without heattreatment were measured. The results are shown in Table 1. In the rowsof MFR (1) and MFR (II) in Table 1, MFR of the film (1) in the adhesivefilm (A2-1) without heat treatment is shown for convenience.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Object to be heat-treated Film FilmAdhesive Adhesive (A1-1) (A1-1) film film (A2-1) (A2-1) Heat treatmenttemperature 285 — 285 — (° C.) Heat treatment time (hr) 24 — 24 — MRF(I) (g/10 min) 16.9 16.9 16.7 16.7 MFR (II) (g/10 min) 1.7 16.9 2.1 16.7MFR (II)/MFR (I) 0.10 1 0.13 1 Linear  50 to 100° C. 175 198 24 19expansion 100 to 150° C. 223 243 23 23 coefficient 150 to 200° C. 283299 23 27 (ppm/° C.) Relative 2.5 GHz 2.85 2.85 dielectric  10 GHz 2.822.82 constant  20 GHz 2.68 2.73

As shown in Table 1, in Ex. 1 in which the heat treatment was conducted,the linear expansion coefficients in the respective temperature rangeslowered as compared with Ex. 2 in which no heat treatment was conducted.Likewise, in Ex. 3 in which the heat treatment was conducted under thespecific conditions, the linear expansion coefficient lowered in a hightemperature range (150 to 200° C.) as compared with Ex. 4 in which noheat treatment was conducted. Further, the relative dielectric constantwas lower at a frequency of 20 GHz in Ex. 3 in which the heat treatmentwas conducted than in Ex. 4 in which no heat treatment was conducted. Itwas found from these results that the electrical properties (lowdielectric constant) of the fluororesin were further improved at highfrequency, by the heat treatment.

Production Example 5

The film (1), a polyimide film having a thickness of 25 μm (manufacturedby Du Pont-Toray Co., Ltd., product name “Kapton 100EN”), anelectrolytic copper foil having a thickness of 12 μm (manufactured byFukuda Metal Foil &Powder Co., Ltd., “CF-T4X-SVR-12”, surface roughness(Rz): 1.2 μm) were laminated in the order of electrolytic copperfoil/film (1)/polyimide film/film (1)/electrolytic copper foil andpressed at a temperature of 360° C. under a pressure of 1.3 MPa for 10minutes to obtain a metal laminate precursor having metal layers on bothsides.

From the metal laminate precursor, the metal layers on both sides wereremoved by etching, and one of the films (1) was separated, and MFR (V)of the film (1) was measured and found to be 16.7 g/10 min.

(Ex. 5, Ex. 6)

The metal laminate precursor obtained in Production Example 5 washeat-treated under each of conditions (temperature and time) asidentified in Table 2 to obtain a metal laminate.

From the metal laminate after the heat treatment, the metal layers onboth sides were removed by etching, and the linear expansion coefficientof the obtained film (1)/polyimide film/film (1) was measured. Theresults are shown in Table 2.

Further, from the metal laminate after the heat treatment, the metallayers on both sides were removed by etching, one of the films (1) wasseparated, and MFR (VI) of the separated film (1) was measured. Theresults are shown in Table 2.

Further, in Ex. 5 and 6, with respect to the film (1), infraredabsorption spectrum analysis was carried out, and it was confirmed thatthe acid anhydride residue derived from NAH remained. For comparison,the above Ex. 4 was also shown in Table 2.

TABLE 2 Ex. 5 Ex. 6 Ex. 7 Object to be heat-treated Metal Metal Adhesivelaminate laminate film precursor precursor (A2-1) Heat treatmenttemperature 260 285 — (° C.) Heat treatment time (hr) 24 24 — MRF (V)(g/10 min) 16.7 16.7 16.7 MFR (VI) (g/10 min) 4.9 1.9 16.7 MFR (VI)/MFR(V) 0.29 0.11 1 Linear  50 to 100° C. 18 19 19 expansion 100 to 150° C.19 21 23 coefficient 150 to 200° C. 17 21 27 (ppm/° C.)

As shown in Table 2, in Ex. 5 and 6 in which the heat treatment wasconducted, the linear expansion coefficients in the respectivetemperature ranges tended to lower as compared with Ex. 4 in which noheat treatment was conducted. Particularly, a reduction in the linearexpansion coefficient in a high temperature region (from 150 to 200° C.)was significant. As a result, in Ex. 5 and 6, the difference in thelinear expansion coefficient among the respective temperature ranges isdecreased by the heat treatment, and the thermal stability of the linearexpansion coefficient was indicated.

(Ex. 7 to 14)

The granules of the fluorinated copolymer (a-1) obtained in ProductionExample 1 were press-molded to obtain a press-molded product of 80 mm×80mm×0.25 mm±0.05. Molding was conducted by using a melt hot pressingmachine “Hot Press Double” (manufactured by TESTER SANGYO CO., LTD.) at350° C. under 10 MPa for a pressing time of 5 minutes.

From the obtained molded product, a plate-shaped sample having a lengthof 30 mm, a width of 5 mm and a thickness of 0.25±0.05 mm was cut outand subjected to a heat treatment under conditions (temperature andtime) in each Ex. as identified in Table 3. With respect to the samplepiece after the heat treatment (corresponding to the material for aprinted circuit board), MFR (II) and the storage elastic modulus weremeasured. In Ex. 14, no heat treatment was conducted, and the storageelastic modulus was measured. The results are shown in Table 3.

(Ex. 15, Ex. 16)

Using a PFA-1 (TFE/perfluoro(alkyl vinyl ether) copolymer, meltingpoint: 305° C., MFR: 13.6 g/10 min, manufactured by Asahi Glass Company,Limited, product name “Fluon PFA 73PT” containing no carbonyl group)instead of the fluorinated copolymer (a-1), a press-molded product wasobtained in the same manner as in Ex. 7 to 14, and a heat treatment wasconducted under conditions (temperature and time) as identified in Table3. With respect to the sample piece after the heat treatment, MFR (II)and the storage elastic modulus were measured. In Ex. 15, no heattreatment was conducted, and the storage elastic modulus was measured.The results are shown in Table 3.

TABLE 3 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex.16 Heat treatment 260 260 285 285 285 285 285 — — 285 temperature (° C.)Heat treatment 24 336 6 12 24 96 336 — — 96 time (hr) MFR (II) (g/10min) 4.6 1 6.2 5.7 4.6 1.9 0.8 16.8 13.6 13.6 MFR (II)/MFR (I) 0.27 0.060.37 0.34 0.27 0.11 0.05 1 1 1 Storage elastic 934 893 807 835 936 846651 527 312 298 modulus at 23° C. (MPa)

As shown in Table 3, in Ex. 7 to 13 in which the heat treatment wasconducted, the storage elastic modulus at 23° C. improved as comparedwith Ex. 14 in which no heat treatment was conducted. The storageelastic modulus is an index for the rigidity as described above. It isindicated that the rigidity increased, and deformation such as warpagetends to be suppressed by conducting the heat treatment under specificconditions.

The storage elastic modulus at high temperature is high when the storageelastic modulus at 23° C. is high, and the storage elastic modulus athigh temperature is low when the storage elastic modulus at 23° C. islow. Accordingly, in Ex. 7 to 13, it is indicated that the rigidity athigh temperature was also excellent, the linear expansion coefficient athigh temperature lowered, and deformation such as warpage at hightemperature was less likely to occur.

Further, in Ex. 16 in which PFA-1 having no carbonyl group was used andthe heat treatment was conducted under the specific conditions, thestorage elastic modulus rather decreased and was not improved ascompared with Ex. 15 in which no heat treatment was conducted. It isconsidered that since PFA-1 contains no carbonyl group-containing group,a crosslinked structure was not formed even when a heat treatment wasconducted.

INDUSTRIAL APPLICABILITY

The printed circuit board obtained by the production method of thepresent invention is useful as a flexible printed circuit board which isrequired to have a high level of electrical reliability.

This application is a divisional of U.S. application Ser. No.15/786,876, filed on Oct. 18, 2017, which is a continuation of PCTApplication No. PCT/JP2016/063760, filed on May 9, 2016, which is basedupon and claims the benefit of priority from Japanese Patent ApplicationNo. 2015-096471 filed on May 11, 2015. The contents of thoseapplications are incorporated herein by reference in their entireties.

1. A material for a printed circuit board, which is a film consisting ofa fluorinated resin layer, wherein the fluorinated resin layer comprisesa composition comprising a fluorinated copolymer having at least onefunctional group selected from the group consisting of a carbonylgroup-containing group, a hydroxy group, an epoxy group and anisocyanate group, has a melt flow rate of at most 15 g/10 min measuredat 372° C. under a load of 49N, and has a storage elastic modulus of atleast 650 MPa.
 2. The material according to claim 1, wherein thefluorinated copolymer has at least a carbonyl group-containing group asthe functional group, and the carbonyl group-containing group is atleast one selected from the group consisting of a group having acarbonyl group between carbon atoms in a hydrocarbon group, a carbonategroup, a carboxy group, a haloformyl group, an alkoxycarbonyl group andan acid anhydride residue.
 3. The material according to claim 1, whereinthe content of the functional group is from 10 to 60,000 groups per1×10⁶ carbon atoms in the main chain of the fluorinated copolymer.
 4. Amaterial for a printed circuit board, which is an adhesive film having afluorinated resin layer directly laminated on at least one side of aheat resistant resin film, wherein the fluorinated resin layer comprisesa composition comprising a fluorinated copolymer having at least onefunctional group selected from the group consisting of a carbonylgroup-containing group, a hydroxy group, an epoxy group and anisocyanate group, and has a melt flow rate of at most 15 g/10 minmeasured at 372° C. under a load of 49N, and the linear expansioncoefficient of the material for a printed circuit board at from 150 to200° C. is within a range of from 0 to 25 ppm/° C.
 5. The materialaccording to claim 4, wherein the fluorinated copolymer has at least acarbonyl group-containing group as the functional group, and thecarbonyl group-containing group is at least one selected from the groupconsisting of a group having a carbonyl group between carbon atoms in ahydrocarbon group, a carbonate group, a carboxy group, a haloformylgroup, an alkoxycarbonyl group and an acid anhydride residue.
 6. Thematerial according to claim 4, wherein the content of the functionalgroup is from 10 to 60,000 groups per 1×10⁶ carbon atoms in the mainchain of the fluorinated copolymer.
 7. A metal laminate comprising anadhesive film having a fluorinated resin layer directly laminated on atleast one side of a heat resistant resin film, and a metal layerdirectly laminated on the at least one fluorinated resin layer, whereinthe fluorinated resin layer comprises a composition comprising afluorinated copolymer having at least one functional group selected fromthe group consisting of a carbonyl group-containing group, a hydroxygroup, an epoxy group and an isocyanate group, and has a melt flow rateof at most 15 g/10 min. measured at 372° C. under a load of 49 N, andthe linear expansion coefficient of the adhesive film at from 150 to200° C. is within a range of from 0 to 25 ppm/° C.
 8. The materialaccording to claim 7, wherein the fluorinated copolymer has at least acarbonyl group-containing group as the functional group, and thecarbonyl group-containing group is at least one selected from the groupconsisting of a group having a carbonyl group between carbon atoms in ahydrocarbon group, a carbonate group, a carboxy group, a haloformylgroup, an alkoxycarbonyl group and an acid anhydride residue.
 9. Thematerial according to claim 7, wherein the content of the functionalgroup is from 10 to 60,000 groups per 1×10⁶ carbon atoms in the mainchain of the fluorinated copolymer.